Digital camera modules are currently being incorporated into a variety of portable electronic devices. Such devices include for example mobile phones (e.g. smartphones), personal data assistants (PDAs), computers, and so forth. Digital camera modules for use in portable devices have to meet certain requirements such as good quality imaging, small footprint, as well as low weight.
Several techniques for small digital camera modules providing good quality imaging are described in WO14083489 and WO14199338, both assigned to the assignee of the present application.
According to the technique described in WO14083489, a multi-aperture imaging system comprises a first camera with a first sensor that captures a first image and a second camera with a second sensor that captures a second image. The two cameras have either identical or different FOVs. Either image may be chosen to be a primary or an auxiliary image, based on a zoom factor. An output image with a point of view determined by the primary image is obtained by registering the auxiliary image to the primary image.
The technique described in WO14199338 relates to a dual-aperture zoom digital camera operable in both still and video modes. The camera includes Wide and Tele imaging sections with respective lens/sensor combinations and image signal processors and a camera controller operatively coupled to the Wide and Tele imaging sections. The controller is configured to combine in still mode at least some of the Wide and Tele image data to provide a fused output image from a particular point of view, and to provide, without fusion, continuous zoom video mode output images, each output image having a given output resolution. The video mode output images are provided with a smooth transition when switching between a lower zoom factor (ZF) value and a higher ZF value or vice versa. At the lower ZF the output resolution is determined by the Wide sensor, while at the higher ZF value the output resolution is determined by the Tele sensor.
General Description
There is a need in the art for a novel camera module for use in modern portable electronic devices, such as smart phones, laptops, notepads, etc.
As noted above, the requirements for the camera modules for use in such devices are related to the size, weight and image quality of the camera. Moreover, these requirements become more essential when the camera module is to be installed within the portable device, unlike other external camera units attachable to the portable device. In the case of an internal (integral) camera unit, the dimensions of the camera optics should be as small as possible in order to be suitable to operate with commonly used detectors and to fit the thickness of the device in which the camera is installed (preferably without protruding from the device's casing), while the trend in such devices is to reduce the thickness as much as possible.
This problem is even more crucial when using, in a portable device, a lens with a long length with a fixed and relatively high zooming effect. Considering for example the dual-aperture zoom digital camera described in above-indicated publications WO014083489 and WO014199338 mentioned above, it utilizes Wide and Tele imaging channels which provide advanced imaging capabilities such as zoom and image quality by image fusion between the two channels.
One of the problems with dual-aperture zoom cameras relates to the dimensions (heights) of Wide and Tele cameras along the optical axis. Such dimensions depend on total track lengths (TTLs) of the Tele and Wide lenses used in the respective imaging channels.
As schematically illustrated in FIG. 1B, the TTL is typically defined as the maximal distance between the object-side surface of the lens module and an image plane IP defined by such a lens module (where the sensing surface of a camera detector is placed). In most miniature lenses, the TTL is larger than the effective focal length (EFL) of the lens module, which is equal to the distance between the effective principal plane of the lens and its focal plane (which substantially coincides with image plane IP).
With regard to the term effective principal plane, the following should be understood. Generally, the lens (or lens module) has front and rear principal planes, which have the property that a ray emerging from the lens appears to have crossed the rear principal plane at the same distance from the axis that that ray appeared to cross the front principal plane, as viewed from the front of the lens. This means that the lens can be treated as if all of the refraction occurred at the principal planes. The principal planes are crucial in defining the optical properties of the system, since it is the distance of the object and image from the front and rear principal planes that determine the magnification of the system. The principal points are the points where the principal planes cross the optical axis.
Considering dual-aperture optical zoom in a mobile phone (e.g. a smartphone) with the typically used lenses, i.e. typical TTL/EFL ratio of about 1.3, the Wide and Tele lenses would have TTLs of about 4.55 mm and 9.1 mm, respectively. This will result in undesirably long camera modules for use in such a smartphone device.
Further, the difference in the TTLs of the Wide and Tele lens modules can cause shadowing and light-blocking problems. Reference is made to FIG. 1A schematically illustrating that part of incoming light incident on the “higher” lens does not reach the “shorter” lens. In this connection, one should keep in mind that a distance between the Tele and Wide lens modules should be as small as possible to meet the overlapping/common FOVs as well as footprint requirements for the camera unit in a portable device.
Another part of the presently disclosed subject matter is associated with the implementation of standard optical image stabilization (OIS) in a dual-aperture zoom camera. Standard OIS compensates for camera tilt (“CT”) by a parallel-to-the image sensor (exemplarily in the X-Y plane) lens movement (“LMV”). Camera tilt causes image blur. The amount of LMV (in mm) needed to counter a given camera tilt depends on the cameras lens EFL, according to the relation LMV=CT*EFL where “CT” is in radians and EFL is in mm. Since, as shown above, a dual-aperture zoom camera may include two lenses with significantly different EFLs, it is impossible to move both lenses together and achieve optimal tilt compensation for both Tele and Wide cameras. That is, since the tilt is the same for both cameras, a movement that will cancel the tilt for the Wide camera will be insufficient to cancel the tilt for the Tele camera. Similarly, a movement that will cancel the tilt for the Tele camera will over-compensate the tilt cancellation for the Wide camera. Assigning a separate OIS actuator to each camera can achieve simultaneous tilt compensation, but at the expense of a complicated and costly camera system.
Thus, for both a single-aperture or multi-aperture (dual) camera unit, the use of a telephoto lens would be advantageous, as such a telephoto lens provides reduced TTL while enabling to maintain the relatively high EFL required for the Tele lens, i.e. for telephoto lens TTL<EFL. However, the dimensions of conventional lenses in which the telephoto condition is satisfied do not allow them to be used as integral lenses fully embedded in a thin portable device. The telephoto lens module, in order to be used as an integral lens in a modern portable device, has to satisfy the telephoto condition (i.e. TTL<EFL) while the lens module is to be as short as possible (along the optical path of light passing through it) allowing it to be fully fitted within the portable device casing.
Accordingly, a miniature telephoto lens module is disclosed which is designed with the desired dimensions to enable its integration within a portable device. According to some examples of the presently disclosed subject matter, the miniature telephoto lens module (or telephoto lens unit) is designed to be completely integrated within the casing of a conventional Smartphone, i.e. without protruding therefrom. The disclosed telephoto lens module has a total track lens (TTL) smaller than an effective focal lens (EFL) thereof, and is configured such that its dimension along the optical axis is desirably small, i.e. about 4-15 mm or less (e.g. suitable to be fitted in a portable device having a casing as small as 4 mm).
The telephoto lens unit comprises multiple lens elements made of at least two different polymer materials having different Abbe numbers. The multiple lens elements comprise a first group of at least three lens elements being a telephoto lens assembly, and a second group of at least two lens elements being a field lens assembly.
The first group of lens elements comprises, in order from the object plane to the image plane along an optical axis of the telephoto lens unit: a first lens having positive optical power and a pair of second and third lenses having together negative optical power such that said telephoto lens assembly provides a telephoto optical effect of said telephoto lens unit and wherein said second and third lenses are each made of one of said at least two different polymer materials having a different Abbe number, for reducing chromatic aberrations of said telephoto lens. The second group of lens elements is configured to correct field curvature of said telephoto lens assembly, and said field lens module comprises two or more of said lens elements made of the different polymer materials respectively having different Abbe numbers, and configured to compensate for residual chromatic aberrations of said telephoto lens assembly dispersed during light passage through an effective gap located between the telephoto and field lens assemblies. The effective gap is larger than ⅕ of the TTL of the telephoto lens unit, thereby allowing sufficient field separation for reducing chromatic aberration.
Various examples disclosed herein include an optical lens unit comprising, in order from an object side to an image side: a first lens element with positive refractive power having a convex object-side surface, a second lens element with negative refractive power having a thickness d2 on an optical axis and separated from the first lens element by a first air gap, a third lens element with negative refractive power and separated from the second lens element by a second air gap, a fourth lens element having a positive refractive power and separated from the third lens element by an effective third air gap, and a fifth lens element having negative refractive power, separated from the fourth lens element by an effective fourth air gap, the fifth lens element having a thickness d5 on the optical axis.
An optical lens unit may further include a stop, positioned before the first lens element, a glass window disposed between the image-side surface of the fifth lens element and an image sensor with an image plane on which an image of the object is formed.
Each lens element has two surfaces, each surface having a respective diameter. The largest diameter among all lens elements is defined as an “optical diameter” of the lens assembly.
As disclosed herein, TTL is defined as the distance on an optical axis between the object-side surface of the first lens element and an image plane where the image sensor is placed. “EFL” has its regular meaning, as mentioned above. In all embodiments, TTL is smaller than the EFL, i.e. the TTL/EFL ratio is smaller than 1.0. In some embodiments, the TTL/EFL ratio is smaller than 0.9. In an embodiment, the TTL/EFL ratio is about 0.85. According to some examples the lens assembly has an F number F#<3.2.
According to an example disclosed herein, the focal length of the first lens element f1 is smaller than TTL/2, the first, third and fifth lens elements have each an Abbe number (“Vd”) greater than 50, the second and fourth lens elements have each an Abbe number smaller than 30, the first air gap is smaller than d2/2, the effective third air gap is greater than TTL/5 and the effective fourth air gap is smaller than 1.5d5TTL/50. In some embodiments, the surfaces of the lens elements may be aspheric.
In the optical lens unit mentioned above, the first lens element with positive refractive power allows the TTL of the lens unit to be favorably reduced. The combined design of the first, second and third lens elements plus the relative short distances between them enable a long EFL and a short TTL. The same combination, together with the high dispersion (low Vd) for the second lens element and low dispersion (high Vd) for the first and third lens elements, also helps to reduce chromatic aberration. In particular, the ratio TTL/EFL<1.0 and minimal chromatic aberration are obtained by fulfilling the relationship 1.2×|f3|>|f2|>1.5×f1, where “f” indicates the lens element effective focal length and the numerals 1, 2, 3, 4, 5 indicate the lens element number.
The relatively large effective gap between the third and the fourth lens elements plus the combined design of the fourth and fifth lens elements assist in bringing all fields' focal points to the image plane. Also, because the fourth and fifth lens elements have different dispersions and have respectively positive and negative power, they help in minimizing chromatic aberration.
The telephoto lens module disclosed herein may be advantageously adapted to be incorporated in a mobile phone camera that uses a typical ¼′ or ⅓′ image sensor. For example, to be competitive with known mobile phone cameras with ¼′ image sensors, it would be advantageous for the TTL of the telephoto lens module to be smaller than 5.5 mm and the largest lens diameter to be smaller than 4 mm. To be competitive with known mobile phone cameras with ⅓′ image sensors, it would be advantageous for the TTL of the telephoto lens module to be smaller than 6.5 mm and the largest lens diameter to be smaller than 5 mm.
Accordingly to an example of the presently disclosed subject matter there is provided an optical lens unit configured to provide an image on an entire area of a ¼″ image sensor, the lens unit comprising five lens elements and having a TTL smaller than 5.5 mm, an EFL larger than 5.9 mm, and an optical diameter smaller than 4 mm.
Accordingly in another example of the presently disclosed subject matter there is provided an optical lens unit operative to provide an image on an entire area of a ⅓″ image sensor, the lens unit comprising five lens elements and having a TTL smaller than 6.2 mm, an EFL larger than 6.8 mm, and an optical diameter smaller than 5 mm.
Also, as mentioned above, according to the presently disclosed subject matter it is suggested to have all lens elements made of polymer material such as plastic. While lenses made of polymer material are advantageous for reducing the price tag of the telephoto lens module as well as its weight, there are very few polymer materials which are suitable for this purpose. This is different to glass lenses which can be made of a variety of different glass materials, each characterized by a different Abbe number. The scarcity in polymer materials presents a challenge when designing lenses for a telephoto lens module. This challenge is at least partly due to the limitation in possible combinations of different lenses with different Abbe numbers which can be used for the purpose of correcting field curvature and compensating for chromatic aberrations.
Thus, according to one aspect of the presently disclosed subject matter there is provided a mobile electronic device comprising an integrated camera, wherein the camera comprises a Wide camera unit comprising a Wide lens unit, and a Telephoto camera unit comprising a telephoto lens unit, the telephoto lens unit and the wide lens unit having respectively TTL/EFL ratios smaller and larger than 1 and defining separate telephoto and wide optical paths.
In addition to the above features, the mobile electronic device according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (i) to (xvi) below, in any desired combination or permutation:
(i). wherein light receiving outer surfaces of the Wide and Telephoto lens units are located substantially in the same plane, thereby reducing shadowing and light blocking effects therebetween.
(ii). wherein the Wide and Telephoto camera units are mounted on separate printed circuit boards.
(iii). wherein the printed circuit boards are located in different spaced-apart substantially parallel planes.
(iv). wherein the Wide and Telephoto camera units are mounted directly on a single printed circuit board.
(v). wherein the Wide and Telephoto camera units are spaced from one another a distance d of about 1 mm.
(vi). wherein the telephoto lens unit is made of at least two polymer materials.
(vii). wherein the telephoto lens has a total track lens (TTL) not exceeding 15 mm.
(viii). wherein the telephoto lens has TTL less than 10 mm.
(ix). wherein the telephoto lens unit comprises multiple lens elements made of at least two different polymer materials having different Abbe numbers, the multiple lens elements comprise a first group of at least three lens elements configured to form a telephoto lens assembly, and a second group of at least two lens elements configured to form a field lens assembly, wherein the field lens assembly is spaced from the telephoto lens assembly by a predetermined effective gap.
(x). wherein said at least two different polymer materials comprise at least one plastic material with the Abbe number larger than 50, and at least one plastic material with the Abbe number smaller than 30.
(xi). wherein the first group of lens elements comprises, in order from an object plane to an image plane along an optical axis of the telephoto lens unit: a first lens having positive optical power and a pair of second and third lenses having together negative optical power such that said telephoto lens assembly provides telephoto optical effect of said telephoto lens unit, and said second and third lenses are each made of one of said at least two different polymer materials having a different Abbe number, for reducing chromatic aberrations of said telephoto lens; and
the second group of lens elements is configured to correct field curvature of said telephoto lens assembly, and comprises two or more of said lens elements made of the different polymer materials respectively having different Abbe numbers, and configured to compensate for residual chromatic aberrations of said telephoto lens assembly dispersed during light passage through said effective gap between the telephoto and field lens assemblies.
(xii). wherein the first, third and fifth lens elements have each an Abbe number greater than 50, and the second and fourth lens elements have each an Abbe number smaller than 30.
(xiii). wherein the predetermined effective gap is equal to or larger than ⅕ of the TTL of the telephoto lens unit.
(xiv). wherein the lens elements of the field lens assembly are spaced from one another an effective air gap smaller than 1/50 of the TTL of the telephoto lens unit.
(xv). wherein the telephoto lens unit has a TTL smaller than 5.5 mm, an effective focal length (EFL) larger than 5.9 mm, and an optical diameter smaller than 4 mm, thereby enabling to provide an image on an entire area of a ¼″ image sensor.
(xvi). wherein the telephoto lens unit has a TTL smaller than 6.2 mm, an effective focal length (EFL) larger than 6.8 mm, and an optical diameter smaller than 5 mm, thereby enabling to provide an image on an entire area of a ⅓″ image sensor.
According to another aspect of the presently disclosed subject matter there is provided a camera for integrating in a mobile electronic device, the camera comprising a Wide camera unit and a Telephoto camera unit comprising respectively a wide lens unit and a telephoto lens unit having TTL/EFL ratios larger and smaller than 1, respectively, and defining wide and telephoto optical paths.
Wherein according to some examples the lens elements of at least the telephoto lens unit are made of one or more polymer materials.